Telephone system



May 12, 1931. L. H. JOHNSON ETAL TELEPHORB svsrsu Filed Sept. 12, 1929 2 Sheets-Sheet 1 BYWWM ATTORNEY May 12, 1931. L. H. JOHNSON ET AL. I 78 TELEPHONE SYSTEM Filed Sept. 12, 1929 2 Sheets-Sheet 2 [ll-{Y Q, 1 E Q Q g $1 I k Q Q a E] [KO-M //V VE N 70/?5'.

ATTORNEY ground is'notso connected when a call is orig- Patentecl May 12, 1931 LEWIS JOHNSON, or ,MADISON, annsny. Ann RAY, I. sroKnLY, or FLORAlLi SPARK, new YoR n-ssisiqoR-s .ro EL ELEPHQNE LABORATORIES,INCORPORATED,

,or new Yong, a COR-EOBATION on NEWjYOBK ainrinr ionnsy srnm I Application fiie'a sea-saw 12, 1929. Serial 110,392,114.

This invention relatesto telephoneexchange systems and'more' particularly-to measured service for party lines.

.The object of the invention is to minimize the amount of equipment necessary to provide for the selective -operation of the mes-' sage'registers associated with a party line.

'According to thi's'invention two non-polari zed message registers wliich are individual respectively 'to two" stations of a party line are connected to one operating lea-d positive source ofcurr'ent being provided for operatin one of saidr'egisters and a negative source of current being provided for operat& ing the other-ofs'aid registers. Y I

According to another feature of this inven tion unidirectional current flow devices are so connected, in coinbination'with two message registers, to one operating-lead that one of thejegisters is operated by current over this leadin one direction and-the 'otherregister isoperated by current over thisllea'd in the opposite direction. A potential "o'f'the proper polarityis impressed upon the 'operatlng lead" to operate the register which corresponds to the station at which the call has originatedi- '14 and the-terminals withwhich the brushes 1 are in contact, is of the well known Strowger type. The line-finder circuit which may he 1 similar to that disclosed in the co-pending application of Henry Hovland Serial No. 37 4,- j f358, filed June 28,1929, is schematically rep- 7 resented by the'brokenjlines connecting to the brushes-11, 12, 13 and 14:. I 7

Referring to the'drawings' Fig; lf'shows two subscribers stations A and Bicon'nected tof the line 1', the'assoclat'edline circuit 1ncludmg a message. register for each station line-finder-LF and an' identifie'ation triinlr circuit T. Fig; 2 shows aselectorcircuit S, a connector circuit; C, a'called subsoribers-s'tation D,'and an operators position 0. Figs;-

' l 2 together illustrate-asystem in which this invention'is embodied, Fig. 3 shows an alternative arrangement for operatively conff t ing line, with whose terininals the brushes ot; the line-finder LF are in contact, to determine which 'ot the stations on this line necting the individual message registers in the line circuit of a two-party linei he subscribers set at station' A li-s tr: ranged so'that ground is connected to thje line when'thereceiver is removed from thefreceiver hook to 'origina'te a call. *The sub -l scribers set V at station B is arranged so that inated thereat. The line 1 terminates i'ntht banks of line-fi nderswitches, one is I I usefd"for; finding iand' extending tlie li e1] for operating oneof the registers includes a positive' potential and the circuit for operwhen aicall is originated at eitherof sta en's 'Aor B, and'terminates in-the banks (not shown) ofconnector switches, which are used in completing connections when either of stations A or' B is the calledstationl line 1 is also connected through theback con tacts of the cut-oifrelay' lto the windings of theline relay 2 in theusual manner. I The cut-off relay 4 is connected'by the operation of line relay 2 to the sleeve terminal asso-" ciated with the line-terminals ofline l'in the W linje finder and connector banks. A four-thterminal, associated with the line 1 inthe line finder'banks only, is connected to-the messageregisters 9'and 10 of'stations A and B, respectively. The registers 9 and 10 arecon= nected in parallel, a unidirectional current carrying device 7 being in serieswith register 9 and a similar device 8 being inseries with register 10. The devices 7 and 8 are opposite- I ly poled so that the register 9 operates whena positive potential of sufiicientj magnitude is connected to the associated terminal of the f line-finder bank and the register 10 operates when a negativepotentialis connected to this a terminal.

"The line-fin derswitch LF, which is represented schematically by'brushes ll, 12, 13 and 'The trunkicircuit T,-which links-the line- I finder 'LF with its "associated selector S (shown in F i g. 2) is arranged to test the callhas'originated thecall and ifthe call is one, for which a charge 'shou'ld'be made, to selec-1 tiv'ely control the-operation or the c,orr e" sponding message register when the called station answer's. This trunk "circuit is simi- "lar to that disclosed in the abovementioned" Ho'vland'applica'tion except that the circuit ating the other includes a negative poten- The connected to the tip and ringconductors offinder brush; 12, ring conductor of line 1,,

tial, and neither of them includes the sleeve conductor of the line-finder and trunk circuits.

The selector switch S and connector switch C are of, the Strowger type. The selectorcircuit is; shown-in detail but the connector circuit is represented schematically bythe broken lines leading to brushes 71, 72 and 73 of the connector switch. For morecomplete descriptions-of Strowger type selector and connector switches reference maybe-had to pages 53 to inclusive of the second edition of Automatic Telephony by Smith and Campbell.

The operation of the system represented by Figs. 1'1and2 will now be described in detail,v Assume thatia .call'is originated-by of; the/1 line-finders having; access thereto. Assume that the line-finderv LF hunts for; and extends. the line 1 through brushesll and s12 tQ'thetru-nk circuit T,1, and that thecut-ofi relay operatesdn a circuit through sleeve brush 13 to ground -,in*theline-finder circuit. a.

Lineerelay 2 releases whenthe cut-ofi relay operates L and the. cut-oftv relay now" holds through its own front contactr (For-a .de-

tailed. description of the operationof the lineirfindercircuit-reference may *be had. to

the: above ;-mentioned application of Hovland.) 1

With .the. line-finder brushes 11 and 12 the line 1,-.line':;relay1 9 or the trunk 5T open.

ates. in a :circuitwhich 'may be traced from battery-throughits winding, through the-- back contact ofthe lower armature and continuity springs of relay j 29, middle lower. v

back contact of relay 28,*conductor 16, liner.

through the calling subscribers instrument, backover-the.tip-conductor ofline 1,;through line-finder brush 11, conductor 15,:uppen back contact of relay2 8,--back contact of the ner upper back contact -of.- relay 29, lower front-contact of relay 19,.conductorv31,j and through the w-inding of relay 26 to battery. Relay 26 operates thereby connecting ground through its, inner left-hand front. contact, over conductor, 32, through normally closed contacts of both sets of continuity springsof relay 25-, hand through the, normally closed contacts of the, continuity: springs: of

relay 2,2, :to the sleevenconducton 17 of the line-finder LF, so as to hold the cut-oil relay 4 and to prevent the release of the line-finder switch.

The aforementioned operation of relay 19 closesa circuit for operatingthe'line relay-53 of the selector S, this circuit may be traced from battery through the left-hand winding of relay53, inner upper back contact -of-*relay;5t'r,* ring conductor-49, righthand winding ofpolarized supervisory relay 47,- outer lower backcontact of relay 29, lower back contact of relay 21, retard coil 35, upper front contact of relay 19, outer upper backtcontactof relay 29, left-hand winding of relay 47, tip conductor 48, outer upper back contact. of relay 56,. right-hand winding-:ofrelay;53,-upper back contact of the,

11th rotary-step springs,;;.to.-ground. The line'relay 53 .close's-acircuit from battery through ther-winding of relay. 54, frontconground.-- Relayv 54 operates, thereby; contact I of: relay 53, conductor 62, and through the outer-lower back contactof relay 56,1.to'.

necting'groundthrough its rightshand :front F contact to: the; sleeve conductor :51- of, .the trunlnT.

' The aforementionedoperation of relay 19. I

also "closesqa circuit; for" operating relay 20 this c'circuit' maybe tracedwfrom battery through its winding,;hack contact of relay 24,; resistance 33,1.outer zleftfhandback a contact of relay 27, conductor 31, front contact ofrelay 19, and through theinnerup er back contact, of relay 429,; to ground.

20,5and through the inner lowerback contact of relay 29 ,--,toground; 1, Relay' 22 looks through its inner right-hand front contact, throughr-the outerright-hand back contact of relay 275 in parallehwith theleft-h and back contactof'relay 23, conductorBQ-and through the, outer left-handfront'contact of relay 26',

a to ground. I In operating, relay 22 connects sleeve conductor 17, through the front conrelay 26, soas to hold cut-off relay}; and prevent the releasecof the-line-finder switch. Re- 1 E lay 22 alsocloses-a circuihfor operating rela upper continuity springs of relay 29,. andthrough retard coil 30., to ground. Relay 19 closes a circuitfrom ground, through the in-- 27, which may be traced from'battery throng V the winding ;-of .relay 27, outerright-hand front nontactrofarelay .22, over sleeve conductor51; In operating, relay 27 causes the.

releaseof relay 20 and-closeslanobvious cir "cuit-for holding relay, 26'.

elay 20 closes a circuit for operatingrelay 22, which :may bewtracedfrom battery, through the winding of :relay;22,- front contact of relay The circuitathrough; the winding: of the identification-test relay 20.wasclosed as hereinbefore described, so asto be surethat. thisirelayiis incondition to determine which of is closed as hereinafter described. Should called number;

relay 27 fail to operate at this time'the ground connected through the inner-right-hand front contact of relay 26 and the inner left hand back contact of relay 27 to conductor 40 is effective to operate an alarm. Therefore relay 24 is not operated even though the call isnompleted and the-charging circuit is not closed when the connection is released.

When the subscriber at the calling station dials the first digit of the number of the called station, the line relay 19 of trunk T' is alternately released and reoperated each time the subscribers line loop is opened and closed at the dial. 1 Each release andreoperationlof relay 19 opens and closes the bridge through the retard coil 35 (across thetip and ring conductors 18 and 49 of the trunk to the se-' lector S) and the line relay 53 of selector S is alternatelyreleased and reoperated in. response to the dialing of the first digit of the The first release of line relay 19 oft'runk T closes a circuit, for operating relay 21, from battery through the winding of relay 21, outer right-hand front contact of relay 26, back contactof relay 19, and through the inner upper back contact of relay 29 to ground. Relay 21 is slow to release and remains operated until all of the impulses created by the dialingof the first digit have'been received. In operating, relay 21 short-circuits the winding of the retard coil 30, thus reducing the impedanceof the dialing'loop, and alsoshort-circuits the winding of retard coil 35 and resistance 36 to reduce the impedance of the trunk loop to the windings of the line relay 53 of selector S. At the end of the train ofimpulses relay 19 reoperates and relay 21 releases. Resistance 36 is connected from the armature to the backcontact of relay -21to prevent the opening and closing of the trunk loop'when relay 21 re-.

leases Relay 26 is slow to release and holds duringthe receipt of'each train ofpulses which are originated by the dialing ofthe digits of the called stations number.

hen the line relay .53 of selectorS releases upon receipt of the first impulse, a circuit is closed from battery, through the Winch ing of the vertical stepping magnet 58, wind ing of relay .55, left-hand front contact of relay 54, back contact of relay. 53, conductor 62, and through the outer lower back contact of relay 56, to ground.-- The magnet'58' and relay both operate in this circuit; Relay 55-is a slow-to-release relay and remains oper-,-

of selector S up to the first level of bank te'r-' minals; The reoperation of line relay 53 releases themagnet 58. Each successive release and reoperation of relay 53 causes the operation andzrelease of magnet 58. The shaft and'brushes of the selector are therefore raised, step-.by-step, to the level through i springs, front contact of relay 55, and over sleeve conductor 51, to ground at relay 54. Relay 57 locks in a circuit from battery through its winding and the upper contact of the VON springs, through the back contact of the rotary stepping magnet 59, conductor 61, left-hand front contact of relay. 57, and through the outer lower back contact of relay 56, toground. The operation of relay 55 is also effective to connect ground from sleeve conductor51 through a front contact of relay 55 toconductor 52 and thus cause the operation of relay 23 of the trunk circuit T; Relay 23 locks through itsleft-hand front contact, normally closed contacts of the continuity springs of relay 28, and through the right-hand back contactof relay 25, over con-' ductor 34, to ground at relay 26. The operation of relay 23 causes the release of relay 22.

When all of the pulses, originated by the dialing of the first digit of thecalled number through the winding of relay 19, resistance 39,

inner lower front contact of relay 28, inner left-hand front contact of relay 27, over sleeve conductor 51, to ground at relay 54 of selector S, and 0) opens the locking circuit of relay 23. Relay 23 releases since its operating circuit (over conductor 52)"'has been opened by the release of relay55 of selector S. Thereleaseof relay 23 causes the release of relay 28,

whereby conductors 15 I and 16 are disconnectedfrom the winding of relay 20 and're connected to .the windings of line relay 19 and retard coil 30. v

If the call originated at station Athe identification test relay 20 operates during the time that its winding is connected over conductors 15 and 16, through line-finder brushes 11 and 12 and over the tip and ring conductors p of line L 1,1to the identifying ljiground atizthe The release of relay of selectors, after the dialing of the first digit, is also eliective to close a circuit for operating the rotary stepping magnet 59 this circuit may be traced from battery through the winding of magnet 59, right-hand front contact of relay 57, normally closed contact of relay 55, over sleeve conductor 51, to, ground at relay 54. The rotary magnet 59 rotates the shaft of selector S-one step, so that the brushes 63, 64, and 66 make contact with the terminals of the first trunk in the'previously selected level. The operation of the rotary magnet causes the release of relay'57. The release of relay 57 causes the release of the rotary magnet, thereby closing a circuit from battery through the winding of -relay.57, upper contact of the VON springs, back contactof magnet 59, conductor 61, winding of relay 56, lower contact of the llth-rotary-step springs, over conductor 51 to ground at relay 54; Conductor 61 is also connected,through the'innerlower back contact of relay 56 and the sleevebru'sh 65, to.the sleeve terminal of the first trunk in the selected level. If this trunk is idle relay 56 operates and relay '57 does not operate; but if the trunk is busy the Winding of relay 56 is short-circuited by the busyround on the'sleeve terminal so that relay 5 operates and relay 56 does not operate. The'reoperation of relay'57 causes the reoperation of the rotary stepping magnet 59. The alternate operation and release-of relay 57 and magnet 59 continues to advance the brushes of selector S step-by-step from one set of'termin'als to the next until thete'rminals of an idle trunk-are encountered.

The operation of relay 56, when an idle trunkis found, disconnects the tip and ring conductors 48 and 494mm the windings of line relay 53 and extends these conductors through brushes 63and 64 overrtip and ring conductors 67 and 680i the selected trunk to the windings of the line relay (not shown) of connector C. Relay 56 also establishes a temporary busy condition on the test terminal of the selected trunk by connecting the sleeve conductor 51 through the inner lower front contact of relay 56 to the sleeve brush 65. Re-

lay 53 releases thereby causing the release;

ofrrelay 54. iRelayrM. slow. tofrerleese: so that the ground at its 'rlght-hand froirtacontact is not disconnected from sleeve conductor 51 "until suflicient ti'mehss elapsed for the v WVhen the remainingndig-its :o' fe; the

stationsinu-mber are 'dialed by the calling subscriber, linerelay 19 and SlOW tO'Z-I'BIOQSG relay 21 of trunk .T repeat the impulses sever thetrunk conductors 48" and 49 through the selector vcircuit rS, to the line i relay shown)'-of the connector (I. The-connector C :is thus controlled to seleot the terminals of the line 74 of-theicalledistation. jFor ardetailedaexplanation of the operation of the connector circuit reference may be hadito pages 57 a) 61 inclusive-of the second'edition of Automatic Telephony "by lsmi thzzqmd Campbell. g

Assume that the line 743s idiewhenvconnection is established therewitmthatringing potentialis connected ito'thei fine, that the subscriber at the called stationlnswersymd that the call .is one for which thecalling; subscriber shouldbe charged. When the're'ceiver is removed 7 from the "receiver; hook 1 at the called station, the windingsof the line' relay (not shown) of the connectorCarereversed, inthe usual manner, withrespect tothe ti and ring conductors 48and49 ofitheftrun 1 T; and as a'result the current through: the windings of the polarized supervisoryrielay 47 is in the direction to operateithisz'relay. The circuit for operating relay'147 r may be traced from battery through 'one' winding. of the line relay (not shown) of the "connector C over the tip conductor.67,l through'brush 63, outer. upperfront contact of relay 56, conductor 48, left-handiwi ndin of relay "47 outer upper back contact of re ay 29, upper front contact of relay 1-9, retard coil-35, lower back contact of relay 21', outer:lowerback:c0n-

tact of relay 29,right-han'd window of-relay 47, conductor 49, inner .upperfront: contact of relay 56, brush i 64, over the ring conductor 68, and through the other winding of the line relay (not shown) of connector C, to ground. The'talking circuit may at this time be traced from trunk conductors. 15 and 16 through backc'ontacts of relays 28 and 29 and through condensers 37 to the trunk conductors 48 and v 49 which connect to the selectoriS.

The operation of'the supervisory relay 47 closes acircuit for operating relay 24 this circuit may be traced from battery through the winding of rely 24, front contact of relay at relay26 over conductors34and 38 for op-.

16, through the back contacts of relay 28,

front contacts of relay 29, and windingsot supervisory relay 47 to, conductors 48 and 49. The line relay (not shown) of connector 0 is held operated in the circuit which includes the calling line until the'calling subscriber releases the connection. a

. When the calling subscriber; replaces the, receiver on the receiverhook the line relay (not shown) of connector C releases. The connector switch is returned to normal in the usual manner. When the sleeve ground at connector is disconnected frorn'the sleeve terminal" with which brush 65 isin contact, relay 56 of selector S and relay" 27 of trunk T are both released." The release of relay 56 closes a circuit for, operating the release magnet 60 ands electorS is returnedto normal in, theiusual manner Inrreleasing, relay 27 closes a circuitg for operating relay 23;,this circuit may lee-traced from battery through the winding of relay 23, conductor 52, inner left-hand .front. contact of relay 24, middle right-hand back contact of relay27, conductor 38, outerright-hand front Contact of relay 24, and over conductor 34, to ground atrelay 26. Relay23 closes the circuit for operating. relay 28. Relay is slow in releasing so that it holds, after relay 27* releases, until relay 28 operates] Relay 28 prevents the release of relay 26 by closingaholding: circuit which may be traced from battery through the winding-of relay 26, outerlower front contact of-relay 28, right-'handback contact ofrelay 25 andover. conductor 84, to ground at relay 26. The operation of. relay 28 transfers the connectionfrom the calling line, over conductors I15 and '16, to the winding of test relay 20. Since the calling subscriber. has hung'up the receiver test relay, fails. to operate unless groundhas been falsely (or otherwise) connected to the line. If relay 2Q does not op'eratelrelay operatesin a circuit which be; traced from battery through the winding of relay 25, back contact of relay 20, inner upper front: contact o f-re lay 28, inner right -hand back contact fof relay; 27, .and over conductor .3240 ground at relay. 26. "Ifrelay 20 operates the operation of relay'25 is prevented for..rela ty 25 isslow in operating. vIn this casev :the line-finder does not releasegand the groundconnected, through the inner fright-handYfront contact of relay 26 andftheinner left hand-back con: tact of relay {27, to tconductor'40-i is efl'ective tooperatean'alarin T p a i ns e yarc q e a;

24,conductor,18, line-finder brush 14, over conductor 6, through the unidirectional current carrying device 7 and through the winding of message register 9, to ground. If the call originated at station B the charging circuit istracedfrom the negativepole of bat-.

tery 44 through lamp and resistance 46,

outer left-hand back contact of relay 22, outer left-hand front contacts of relays 25 and 24, over conductor 18, through line-finder brush 14, over conductor 6, through the unidirectional. current carrying device 8 and through the winding of message register 1 0,to ground. Relayr25 connects ground through its right-hand front contact to conductor 52 to hold relay 23. This ground connection is extended'from conductor 52 through the inner left-hand front contact of relay24 and the middlerightdiand backcontact of relay 27 to conductor 88 thereby holding relays 24 and 29. If relay22 has been operated relay 25 also connects ground through'the inner left-hand front'contacts of relays .25 and 22 tothe sleeve-conductor 17, in place of the ground over conductor .32. Relay 25 opens. the holding circuit {or relay 26 which is slow in releasing. The release of relay 26 causes the release of relays 22 and 25. ,The release of relay 25 causes the release'of relays 23, 24 and 29. The release of relay 23 causes the release of relay 28. Since relay 26 is slow to release the charging circuit is closed for a sufiicient length of time to insure the opera ation of the calling subscribers register. The release of relay 26 causes the release of cut-ofi relay 4 and causes the' line-finder to be restored to normal.

If a call is completed to a subscriber and no charge' is to -be madefor the call, thepolarized su'pervisory relay 47 is not'operated and-thereforefthe charge controlrelay 24is not operated. Relay 27: holds to the'ground on thesleeve'conductor 51 untilthe connec tion isreleased. Relay 27 holds relay 26,

and relay 26 holds relay 23. Relay 29 is not cause the return of the line-finderf LF to normal.

Ifthe first digit dialedbythe,c al l ing-sub scriber is suchthat the selector Sjseizesan idle trunk; leading to an operators position, the terminal with which the brush 66 makes contact is grounded; conductor 7 8 of the trunk which leads to the-operators position 0] is, therefore, connected to ground 'asindicated; When relay 56 operates, this ground isaconnected through brush 66, lower front contact of relay 56, conductor 50, and through the right-hand back contact ofrelay 23", to the winding of" relay 29. Relay 29 operates thereby extending the connection from the calling line over trunkconductors- 15"and' l6' to trunk conductors 48 and 49 and through the brushes ofselector S to the trunk leading to the operators position. Talking-battery is supplied to the calling station from the operators position; and the current through the windings of the polarized supervisory relay 47 is not effective to operate relay 47 unless the call is further extended bythe o perator,-in which case the operator may reverse the battery connected to. the trunk so as tooperaterelay i7; In the latter case the message register of the callingsubscriberis operated, in the manner hereinbefore described, when the connection is released by the calling subscriber.

. Referring to Fig. 3"the subscribefls stations E and F'are c'onlnectedby the line 10L to terminals in thebanlg of line-finder L'F; the line and cut-ofi'"-relays are notshown but the'line'relay'is'connected'to line l and the cut-ofi relay is connected to sleeve conductor 105 in the usual manner. The message registers 109 and 110 are connected in parallel over conductor 106 tothe fourth terminal associated with theline-lO-l; in the bank of line-finder LF. The unidirectional current carrying device 107 is in'parall'el with the Winding of register 1O9 and the device 10% is inparallelwith the winding of register 1'10 instead of these devices being respectively connected in series with the registers asshown in Fig. 1. This arrange mentcauses-the operation of register 109 when thexpositive charging battery is con, nectedto conductorlOGsince the device 107' ott rs a relati y h ghistan e to theflow ofzcurren d regi te 0 o ot operate since w d g-isw nted y t -r la ively low re is an e whi h ev e 1 8- Q ers t0 he flqwv cu rent. Wh n he pq i ive hars mg at ry sc nnected to. nd c or 06., reg s er 1 0 p rates. in e the. dYQ QQ lQ o fers .ar latively high res st nce athelfiew at current nd, register 1.0 do s .nQt Qp ra e since its. W nding isshuntadfhy the rel tively law res s a hic device, 9 q i rsie as flow of current. 4 h

The invention vis not limited to systems uslng Strowgrtype, or any particular-type,

of current over said conductor to selectivelyv operate saidregistersi 2," In a telephone system, a line, a plurality of subscribers stations permanently "connected to said line, a, message registerindividual to'eachof'said stations, a conductorpermanently connected to aplurality of-said registers, a1posi-tive source-of'current, anegative source of current, means forconnecting-sa-id positive source to said conductor:to--operatc one of said'registers, and means, forconnecting said negative source to saidconductor to operate another of said registers.-

'3: In combination, a plurality of metering devices, a conductor permanently connected to-said metering devices, means forproduoinga current in sai'dconductor, andmeans individual to each'ofsaid devices; for controlling said current-to selectively-operate said devices.

4. In atelephonesystem, metering devices, a conductor permanently connected toa plu-f rality of said devices, means individual to each of said devices for renderingsaid plurality of. devices selectively responsive, to cur-- rents of di'fierenticharacteristios.

5. Ina telephone'system, a line having a plurality of subscribers stations one ofwhich is acalling station, messageregisters one for each ,of saidstations, a conductor common to a plurality ofsaid registers, and means associated with theregister of said calling station for rendering said register responsive to. current of acertain characteristic.

6,; In a telephone system, a linehaving a plurality of subscribers stations, one of Which-is a calling station, a message register for each of said stations, a conductor perman yc e e to sa dj eg st and mean including a unidirectional current carrying device associated with each of said registers for selectively operating the register ofjsai'd calling station.

station, a message register for each of said stations, a conductor permanently connected to said message registers, means for determin ing which of said stations is the calling station, and means including said conductor and a unidirectional current carrying device for selectively operating the register of said calling station.

9. In a telephone system, a line, a plurality of subscribers stations permanently connected to said line, means at each of said stations for distinguishing it from the others, a message register individual to each of said stations, a conductor permanently connected to said registers, means individual to each of said message registers selectively responsive to current in said conductor, means for testing said line to determine which of said stations is the calling station, and means for operating the register of said calling station.

10. In a telephone system, a line, two subscribers stations permanently connected to said line, means at each of said stations for distinguishing it from the other, a message register individual to eachof said stations, a conductor permanently connected to said registers, means associated with one of said registers for rendering said one responsive to current in one direction, means associated with the other of said registers for rendering said other responsive to current in the opposite direction, means including a trunk for extending said line when a call is originated at either of said stations, testing means associated with said trunk for determining which of said stations is the calling station, and means for operating the register of said calling station.

In witness whereof, we hereunto subscribe our names this 10th day of September, 1929.

LEWIS H. JOHNSON. RAY L. STOKELY.

for rendering them 

